Phonon-assisted upconversion photoluminescence in Mn-doped two-dimensional hybrid metal halides

Phonon-assisted upconversion process is one of the important means to generate upconversion photoluminescence (UCPL), and has important applications in laser refrigeration and other fields. However, until now, the studies on UCPL behavior are still insufficient. Herein, this work synthesizes a series of Mn-doped two-dimensional hybrid metal halide (2D HMH) thin films and investigates their optical properties using various spectral techniques. Raman spectroscopic measurement confirms that Mn-doping is achieved via interstitial doping rather than Pb-substitution. By the measurement of the temperature-dependent PL spectrum, it is found that Mn-doping will weaken the thermal expansion effect of 2D HMHs, but will enhance the electron–phonon coupling strength. More importantly, both two-photon-excited and phonon-assisted UCPL are observed in Mn-doped 2D HMHs, with an extremely large phonon-assisted energy gain (approximately 500[Formula: see text]meV). Our experimental results are of significance for designing phonon-assisted UCPL materials and expanding their applications.